A, javascript scripting language used by the browser to parse and execute
1. weakly typed strong typing
weak typing in the definition of a variable declaration is not required when the data type, data type is a variable value determined by the
JavaScript
strongly typed variables in the definition of when it has the data to determine the type of
the Java
int a
2. explain line execution
3. interpreted language corresponding to the language compiler
python c / c ++
translation of a see a later convenient all Translation
efficiency interpreted <compiled
two, JavaScript using
the line 1. The wording handle
2. Internal stylesheet <script> js Code </ Script>
3. Waibuyangshibiao <script src = "js to the end of the file path .js"> </ Script>
4. external introducing foreign import module style
writing time is put css inside the head of
writing JavaScript that can be placed anywhere
on the bottom of the page is best
except in exceptional circumstances
Three, JavaScript code is part of the
basic core syntax
variables: the amount will become
the definition of variables
var keyword to define variables of
var variable name = variable value;
naming the variable name: only letters, numbers, _, $ can not start with a number, not a JavaScript keywords and reserved words
in JavaScript is strictly case sensitive ., for example: var B2, B2 var
var a = 123; in a programming language, a = number for assignment, showing two == Analyzing
the data type of the original data type
number string boolean undefined null
string of numbers defined Boolean space
Reference data types
Object object
Four, JavaScript's Math
plus
1. Any type with string concatenation, are strings splice
2. The number and type Boolean, implicit conversion. True converted into a converted 1.false 0
3. numeric type and not the type of operation (except string Boolean). NAN adding unsuccessful appears
NAN (not a number) is not a number, but it is attributed to the type of number
() performs symbol, there can perform functions (methods)
browser execute JavaScript code to
open a Web page, press F12. Open development . tools to find the console (console) option inside
minus
1. can subtract / multiply / divide would reduce, not subtract / multiply / divide the NaN
2. can subtract / multiply / divide: the Boolean, when the string comparison particular time (the string of numbers all the time)
Five, JavaScript sign
Greater than>
greater than or equal to> =
Less than <
Less than or equal <=
equal ==
not equal! =
More js in two
congruent ===
insufficiency equal! ==
JavaScript, because it is weakly typed, so the definition of variables when not entirely clear data types, data types can be determined only after an assignment
== only to compare the contents inside, not to compare data type
=== content and type will be compared, there is a range on false
! =,! ==
Six, JavaScript logic operation
And: Only when all is true when it is true
Or: at least one of the time it is true true
Non-: negated
Seven, JavaScript bomb box
JavaScript is built inside the housing shells (developer already defined) to a function.
Function is for us to call
three kinds of bomb box
alert box warning
prompt input box pops up
confirm box pops up Cancel
function you want to use, you must call
the implementation symbols, brackets indicates parameter alert ( "hello") // ( ). Content warning box
can receive two parameters. With between parameter "," separated.
The first parameter represents the contents to
the second parameter indicates the default content input box
Enter the pop-up box:
The return value is that you input contents of the box, this value can be assigned to a variable
Built-in functions, the content needs to detect the passed in as a parameter. Only one parameter, it is determined whether a variable is numeric, the return value only boolean var a = 10; var b = "hello"; console.log (isNaN ())
isNaN () is a digital returns false, the number returned is not true var c = isNaN (b); console.log (c) Method of cast: ... will all be converted to a string type number. If not turn, compared with NaN / parseInt () // to an integer, to be converted to what passed as a parameter. After the conversion is completed to return the value of forms, and can intercept interception, it is not taken NaN